The present invention relates to a system for detecting vehicles traveling along a plurality of lanes of a toll road.
In order to collect toll automatically at a tollgate to a toll road, it is necessary to detect any vehicle coming to or passing through the tollgate.
A vehicle detecting system is known which optically detects vehicles passing along the lanes of a toll road. As shown in FIG. 1, the system comprises a gantry 2 and a plurality of optical line sensors 3a to 3g. The gantry 2 straddles the toll road 1, extending across the 3-lane toll road 1. The line sensors 3a to 3g are attached to the lower side of the gantry 2. The sensors 3a is located above the outer boundary of the lane 4a, the sensor 3c above the boundary between the lanes 4a and 4b, the sensor 3e above the boundary between the lanes 4b and 4c, and the sensor 3g above the outer boundary of the lane 4c. The sensors 3b, 3d and 3f are located above the center lines of the lanes 4a, 4b and 4c, respectively. On the surface of the road 1, the view field 3x of each line sensor overlaps half the view field 3x of either adjacent sensor.
When no vehicles are under the gantry 2, the line sensors 3a to 3g get the linear images of the surface of the road 1 at the right angle to the direction of the lanes and convert the linear images into video signals respectively. The video signals are stored in a memory device, so that the signals may be used as reference signals. In this case, above the line sensors can use one dimensional type TV cameras, as well as projecting/receiving light type sensors emitting and scanning light beam.
In operation, the line sensors 3a to 3g get the linear images of the surface of the road 1, and convert them into video signals. These signals are compared with the reference signals to determine whether or not vehicles are on the toll road 1. Assume a vehicle 5 is on the second lane 4b as shown in FIG. 2. In this case, the signal generated by the sensor 3d located above the center line of the second lane 4b and the signals generated by the sensors 3c and 3e located on the sides of the sensor 3d are compared with the three reference signals generated by the sensors 3d, 3c and 3e. The basis of the difference between each signal and the corresponding reference signal is used to detect the vehicle 5. In FIG. 2, S1, S2 and S3 represent the diagrammatically the signal differing sections where the signals generated by the line sensors 3c, 3e and 3d differ from the corresponding reference signals, respectively. The signal the sensor 3d generates when the vehicle 5 goes right below the sensor 3d has a signal differing section which is wider than the section representing the width of the vehicle 5. By contrast, the signals the sensors 3c and 3e generate when the vehicle 5 travels right below the sensor 3d have a signal differing section which is just about half the section representing the width of the vehicle 5. This is because the view fields 3x of the sensors 3c and 3e each overlap half the view field 3x of the sensor 3d on the surface of the road 1 and get the image of the vehicle 5 sideways. Hence, the width 6 of the vehicle 5 can be detected from a logical product of the signal differing sections S1, S2 and the signal differing section S3.
Unless the width 6 of the vehicle 5 is extremely small, it can be accurately detected a logical product of the signal differing sections S1, S2 and the section S3. Even the width of a motorcycle, which is relatively small, can be accurately detected unless the motorcycle is located right below any one of the line sensors 3a to 3g.
But the conventional vehicle-detecting system may fail to detect a motor cycle, when a motorcycle 5a is traveling, almost along the center line of the lane 4b as is illustrated in FIG. 3, or virtually along the boundary between the view fields of the line sensors 3c and 3e. If this is the case, the signal differing section S3 of the signal generated by the sensor 3d is large, but the sections S1 and S2 are very small since the widths of signal 7 detecting a motorcycle 5a by the sensors 3c and 3e are small. Consequently, the width 6 determined by processing the signals is therefore less than the actual width of the motor cycle 5a, or the motor cycle 5a may not be detected.
The system shown in FIG. 1 may detects fallen leaves, trash or the like, which happen to be on the toll road 1. In this case, the system generates and supplies a vehicle-detection signal, though no vehicles are passing under the gantry 2. The vehicle-detecting system has but a low operating reliability.
Earth or sand may fall from a damp track onto the road 1 and may spread over the surface of the road 1. The vehicle-detecting system detects the earth or sand and generates a false vehicle-detection signal. In view of this, too, the reliability of the conventional vehicle-detecting system is insufficient.